Mass transfer phenomena in fluidized beds with horizontally immersed membranes: A numerical investigation. (14th December 2018)

• Record Type: Journal Article
• Authors: Voncken, R.J.W.; Roghair, I.; van Sint Annaland, M.
• Is Part Of: Chemical engineering science. Volume 191(2018)
• Page Start: 369
• Page End: 382
• Publication Date: 2018-12-14
• Subjects: Mass transfer -- Fluidized bed -- Membranes -- Two-Fluid Model -- Computational Fluid Dynamics; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2018.07.005
• Languages: English
• ISSNs: 0009-2509

Abstract

Graphical abstract: Highlights: Design guidelines for horizontal membrane tube banks in fluidized beds are given. The flux around a horizontal membrane is lowest on top and highest at the bottom. Membranes near bed walls perform worse due to densified zones and gas back-mixing. Removing membranes near the walls improves the average performance per membrane. A too large distance between the membranes and wall results in gas bypassing. Abstract: Mass transfer phenomena in gas-solid fluidized beds with horizontally immersed membrane tube banks in different configurations were investigated using a Two-Fluid Model, considering the case of a binary hydrogen/nitrogen gas mixture fed to a 2D fluidized bed where hydrogen was extracted via hydrogen perm-selective membranes. The simulations showed that the hydrogen flux is strongly non-uniform over the radius of the membranes. The hydrogen flux is lowest on top of the membranes and highest at the bottom of the membranes, which is caused by the formation of densified zones on top of the membranes and the fact that the membranes shield their own top side from hydrogen replenishment. Also, in systems with membrane tube banks, the performance of individual membranes differs significantly. The membranes located near the bed walls perform considerably worse, because of downwards solids flow near the walls, resulting in more densified zones and gas back-mixing. The average hydrogen recovery per membrane is highest for the cases with a staggered tube bank configuration and without membranes positioned close to the bed walls. In-line tube bank configurations suffer from gas channeling, reducing the hydrogen recovery per membrane. The membrane tube banks also significantly improve the bed hydrodynamics by enhanced bubble-breakage, decreasing the bubble size to approximately the membrane pitch.